In a conventional power amplifier, a plurality of heat sinks are installed on the outer circumferential surface of a center sleeve. Furthermore, a plurality of substrates are accommodated inside the center sleeve. A power transistor is installed on a base section of a heat sink. The terminals of the power transistor are connected to the substrate (see, for example, PTL 1).
Furthermore, in a conventional cooling structure of an electric-powered turbocharger for an engine, the circuit components of the inverter are divided respectively in accordance with the respective phases of u, v, w, and are accommodated in individual substrates for each phase. Furthermore, the substrates are installed on the inner circumference of a cylinder having three or more surfaces having good thermal conductivity (heat sinks) (see, for example, PTL 2).